This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The aim of this study was to assess the effects of nutrient ingestion, dietary protein intake, age, and sex on the fractional synthesis rate (FSR) of albumin. Thirty-six healthy free-living individuals (8 females and 10 males aged 21-43 y and 9 females and 9 males aged 63-79 y) completed three 18-d periods of controlled feeding with protein intakes of 125% (P125, 1.00 g protein x kg(-1) x d(-1)), 94% (P94, 0.75 g protein x kg(-1) x d(-1)), and 63% (P63, 0.50 g protein x kg(-1) x d(-1)) of the recommended dietary allowance. On d 12 of each trial, postabsorptive (PA) serum albumin concentration was determined and PA and postprandial (PP) albumin FSR were estimated from the rate of l-[1- 13C] leucine incorporation into plasma albumin during an 8-h infusion.